1. Technical Field
Example embodiments of the present invention relate in general to a wireless communication system and more specifically to a wireless communication method and apparatus using adaptive transmission polarization control, which maximize efficiency in using wireless resources.
2. Related Art
Wireless resources used in a general mobile communication system include frequency, space, time, polarization, etc. At present, mobile communication systems use orthogonal frequency division multiple access (OFDMA) technology, multiple-input multiple-output (MIMO) technology, and time division multiple access (TDMA) technology for efficiently using wireless resources such as frequency, space, time, etc.
However, in order to satisfy the exponentially increasing demand for wireless data, it is necessary to develop additional wireless resources other than the existing frequency, space, and time resources, and efficiently use the resources.
Therefore, it is becoming increasingly necessary to develop technology that increases a transmission capacity by more actively using a polarization resource, which is restrictively used in existing mobile communication systems, as in polarization diversity.
A wireless channel causes polarization spread (PS) in which a signal transmitted by a transmission apparatus in a certain polarization mode is changed to various polarization modes by multi-path fading and transferred to a reception apparatus.
Moreover, when the polarization of a transmission signal transferred to a reception apparatus is not matched with a polarization mode of a reception apparatus antenna, polarization mismatch loss (PML) occurs.
Existing mobile communication systems obtain a diversity gain using polarization diversity in a wireless channel environment where PS is very severe, but performance is degraded by PML in a wireless channel environment where PS is not severe. Therefore, a method is required for improving a transmission capacity and minimizing the degradation of performance due to PS and PML that occur in a wireless channel.
To prevent distortion such as PS and PML that occur in a wireless channel, a precoding technique is required in which a transmission apparatus distorts a transmission signal in advance and transmits the distorted signal to minimize channel distortion. To precode a transmission signal, a transmission apparatus and a reception apparatus need to know polarization channel state information (PCSI) therebetween in advance.
In a downlink especially, a transmission apparatus (for example, a base station) needs to know downlink PCSI from a transmission antenna of the transmission apparatus to a reception antenna of a terminal in advance.
In a wireless communication system using frequency division duplexing (FDD), a downlink and an uplink use different frequency bands, and thus, in order for a transmission apparatus to know PCSI of the downlink in advance, a reception apparatus needs to estimate a downlink polarization channel state and feedback-transfer the estimated downlink polarization channel state to the transmission apparatus.
A reception apparatus needs many uplink resources for feeding back PCSI to a transmission apparatus, and thus, an effective feedback method that transfers PCSI to the transmission apparatus using minimum feedback information is required.
However, considering the development direction of mobile communication systems, the number of transmission antennas inevitably increases for MIMO technology, and thus, PCSI that a reception apparatus needs to feed back to a transmission apparatus is predicted to rapidly increase.
Accordingly, feedback technology for transferring PCSI to a transmission apparatus using only limited feedback information is required.